A283486 Number of k such that sigma(k) = 2n where sigma(m) = A000203(m) is the sum of the divisors of m.

0, 1, 1, 1, 0, 2, 1, 0, 2, 1, 0, 3, 0, 1, 1, 2, 0, 1, 1, 1, 3, 1, 0, 3, 0, 0, 2, 2, 0, 3, 1, 0, 0, 1, 0, 5, 1, 0, 1, 2, 0, 3, 0, 0, 3, 0, 0, 4, 2, 0, 1, 2, 0, 2, 1, 1, 2, 0, 0, 4, 0, 2, 2, 2, 0, 2, 0, 0, 1, 2, 0, 5, 0, 0, 1, 2, 0, 2, 1, 1, 1, 1, 0, 6, 0, 0, 1, 1, 0, 4, 2, 0, 2, 0, 0, 5

Offset

1,6

Comments

First occurrence of k: 1, 2, 6, 12, 48, 36, 84, ...

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Formula

a(n) = A054973(2n) - Michel Marcus, Mar 08 2017.

Example

a(12) = 3 because sigma(14) = 1 + 2 + 7 + 14 = 24, sigma(15) = 1 + 3 + 5 + 15 = 24 and sigma(23) = 1 + 23 = 24.

Prog

(PARI) first(n)=my(v=vector(n), t); for(k=1, 2*n-1, t=sigma(k)/2; if(t<=n && denominator(t)==1, v[t]++)); v \\ Charles R Greathouse IV, Mar 08 2017

Crossrefs

Cf. A000203, A054973, A060658.

Sequence in context: A110658 A002188 A128313 * A330759 A216607 A025672

Adjacent sequences: A283483 A283484 A283485 * A283487 A283488 A283489

Keyword

nonn

Author

Juri-Stepan Gerasimov, Mar 08 2017

Extensions

a(96) corrected by Charles R Greathouse IV, Mar 08 2017

Status

approved